If you were guaranteed to succeed, what would you be doing?

Someone asked me recently, if you were guaranteed to succeed with anything you wanted to do, what would you be doing?
Well the answer to that only took me a few minutes to come up with, it was very close to the surface.  Is it what I'm now doing?  Not entirely.
Why aren't I doing it then, if its something I really would like to be doing?  Fear of failure?  Fear of ridicule?  Knowing that there's lots of other people around already doing it.  They'be been doing it for longer.  They're possibly more qualified, more experienced.  Why would people want to come to me?  I haven't even written a book yet!
I generally feel that I'm a fairly confident person in most areas of my life but I was surprised at my lack of confidence and vulnerability at the thought of putting myself out there in the public arena, offering new services to the public.  I've even read the book, "Feel the fear and do it anyway"
I'm sure that this is a very human condition, and that I'm not alone.  I think that fear of failure and ridicule is very commonplace.  I then remind myself that a lot of the well known inspirational people out there, 2 of whom immediately spring to mind - JKRowling and Henry Ford, (I dont know why I picked those 2!).  JK Rowling had numerous rejections before her book was published and Henry Ford had many setbacks - the rest is history as they say.
It feels easier to carry on doing what I'm currently doing (and that is fine as I do still really enjoy my work and plan to continue in any case).  But there is a passion inside me that wants to branch out.  So even though I feel vulnerable, I also feel like I have to follow that as I start feeling miserable every time I try to ignore this part of me.  It feels like this is part of my life purpose.  Maybe I just like challenging myself and don't just want an easy life!